unit CRC32;

interface

uses
  Windows,
  Forms,
  SysUtils,
  Classes;

var
  Table:Array[0..255] of DWORD;

  procedure GetCRC32File(FileName:string;var CRC32:DWORD);
  function GetCrc32Str(s: string; Seed: LongInt):string;

  procedure MakeTable();

implementation

procedure MakeTable();
var
  i, j, Crc:integer;
begin
  for i:= 0 to 255 do
    begin
      Crc := i;
      for j := 0 to 7 do
        begin
          if (Crc and 1) <> 0 then
            Crc:=(Crc shr 1) xor $EDB88320
          else
            Crc:=Crc shr 1;
        end;
      Table[i]:=Crc;
    end;
end; 

procedure GetCRC32File(FileName:string;var CRC32:DWORD);
var
  F:file;
  BytesRead:DWORD;
  Buffer:array[1..65521] of Byte;
  i:Word;
begin
  MakeTable();
  FileMode := 0;
  CRC32 := $ffffffff;
  {$I-}
  AssignFile(F,FileName);
  Reset(F,1);
  if IoResult = 0 then
    begin
      repeat
      BlockRead(F, Buffer, Sizeof(Buffer), BytesRead);
      for i := 1 to BytesRead do
        CRC32 := (CRC32 shr 8) xor Table[Buffer[i] xor (CRC32 and $000000ff)];
      Application.ProcessMessages;
      until BytesRead = 0;


    end;
  CloseFile(F);
  {$I+}
  CRC32 := not CRC32;
end;
    
function GetCrc32Str(s: string; Seed: LongInt):string;
var
  Count: Integer;
  CrcVal: LongInt;
begin
  MakeTable();
  CrcVal := Seed;
  for Count := 1 to Length(s) do
    CrcVal := Table[Byte(CrcVal xor DWORD(Ord(s[Count])))] xor ((CrcVal shr 8) and $00FFFFFF);
  Result := IntToHex(not(CrcVal), 8);
end;


initialization
  MakeTable;

end.
